1. Field of the Invention
This invention relates to a connector and a signal transmission method using the same and, in particular, to a differential signal connector for use in connecting transmission lines for transmitting a differential signal pair and a signal transmission method using the differential signal connector.
2. Description of Related Art
There is known a differential transmission method of transmitting a differential signal pair comprising a pair of opposite-phase signals on paired two signal lines. The differential transmission method is capable of achieving high-speed data transmission and, therefore, is recently put into practical use in various fields.
For example, in case where the differential transmission method is used in data transmission between a device and a liquid crystal display, each of the device and the liquid crystal display is provided with a display port connector designed in conformity with a display port standard. As the display port standard, VESA Display Port Standard 1.0 and Version 1.1a thereof are known.
The display port connector is one type of a differential signal connector and has a first connection side for connection with a connecting object and a second connection side for connection with a printed board of the device or the liquid crystal display. The first connection side has a structure strictly determined by the display port standard because of the relationship with the connection object. On the other hand, the second connection side has a structure which is relatively free. The differential signal connector of the type is disclosed in Japanese Patent No. 4439540 (Patent Document 1) (corresp. to US2008/0014803A1).
As illustrated in FIG. 9, the connector disclosed in Patent Document 1 has, as a lower contact group, two pairs of signal contacts 121 and a plurality of ground contacts 122 arranged on opposite sides of each pair of the signal contacts 121.
On the first connection side, contacting portions 121A of the signal contacts 121 and contacting portions 122A of the ground contacts 122 are arranged in a single row at a predetermined distance D1 from one another, as shown in FIG. 9.
On the second connection side, terminal portions 121B of the signal contacts 121 are arranged in a first row R1 while terminal portions 122B of the ground contacts 122 are arranged in a second row R2 which is shifted from the first row R1.
With the above-mentioned arrangement, a distance D2 between the terminal portions 121B and 122B is greater than the distance D1 between the contacting portions 121A and 122A. Thus, it is intended to simultaneously achieve reduction in size of the connector and good mountability of the terminal portions 121B and 122B to through holes (not shown) which require a predetermined size and an arrangement at a predetermined distance.
However, in the connector disclosed in Patent Document 1, the terminal portions 121B of the signal contacts 121 and the terminal portions 122B of the ground contacts 122 are arranged in the different rows R1 and R2, respectively, and the distance D2 between the terminal portions 121B and 122B is wide. Therefore, characteristic impedances around the terminal portions 121B and 122B are higher than those around the other portions. In this event, characteristic impedance matching is difficult to achieve. This results in a problem that high-speed signal transmission (for example, transmission of 10 Gbps or higher-speed signals containing a frequency component at which it is appropriate to treat a connector or a contact as a distribution constant circuit) is difficult.